设a≤x1∫(a,b)|Pn'(x)|dx=|∫(a,x1)Pn'(x)dx|+|∫(x1,x2)Pn'(x)dx|+...+|∫(xk,b)Pn'(x)dx|=|Pn(x1)-Pn(a)|+|Pn(x2)-Pn(x1)|+...+|Pn(xk)-Pn(b)|≤|Pn(x1)|+|Pn(a)|+|Pn(x2)|+|Pn(x1)|+...+|Pn(xk)|+|Pn(b)|≤Max|Pn(x)|+Max|Pn(x)|+...+Max|Pn(x)|=2k*Max|Pn(x)|≤2n*Max|Pn(x)|
